Light
rail and heavy rail grade crossings are regulated by the Federal Transit
Administration. The Federal Transit Adminstration defines two types of grade
crossings: (1) At grade, mixed, and cross traffic crossings, meaning railway
right-of-way over which other traffic moving in the same direction or other
cross directions may pass. This includes city street right-of-way; (2) At
grade with cross traffic crossings, meaning railway right-of-way over which
no other traffic may pass, except to cross at grade-level crossings. This can
include median strip rights-of-way with grade level crossings at intersecting
streets.

Commuter rail grade crossings are regulated by the Federal Railroad Administration. The Federal Railroad Administration defines a grade crossing as a location where a public highway, road, street, or private roadway, including associated sidewalks and pathways, crosses one or more railroad tracks at grade.

Data thresholds changed for certain elements beginning with
2002. The extreme drop in the incidents, injuries, collisions, and not
otherwise classifieds (personal casualties) for 2002 is due to the change of
the incident thresholds, specifically the definition of injuries, in the NTD.
The injury definition was changed for the 2002 revision of the NTD to
coincide with other USDOT modes. Only incidents involving immediate medical
treatment away from the scene now qualify as reportable injuries. Previously,
any reported incident/injury was reported to NTD. It was felt that this
resulted in the collection of claims-based as opposed to safety-based data.